1. Technical Field of the Invention
The present invention relates to an electro-optical device, a method of manufacturing an electro-optical device, a liquid crystal device, a method of manufacturing a liquid crystal device and an electronic apparatus, and particularly to a structure and a manufacturing method for an electro-optical device comprising a wiring substrate connected to an electro-optical panel substrate.
2. Description of the Related Art
At present, liquid crystal devices are widely used for electronic apparatuses such as cellular telephones, potable electronic terminal units, etc. In many cases, a liquid crystal device is used for displaying information by a character, a numeral, a pattern, or the like.
A liquid crystal device generally comprises a pair of liquid crystal substrates each having an electrode formed on the inner side thereof, and a liquid crystal held between the pair of substrates so that the orientation state of the liquid crystal is controlled by controlling the voltage applied to the liquid crystal to modify light incident on the liquid crystal according to the liquid crystal orientation state. The liquid crystal device requires a liquid crystal driving IC, i.e., a semiconductor chip, for controlling the voltage applied to the liquid crystal, the IC being mounted directly on one of the liquid crystal substrates or indirectly thereon through a mounting structure such as a flexible wiring board, or a printed circuit board.
In connecting the liquid crystal driving IC indirectly to one of the liquid crystal substrates through the mounting structure, for example, the liquid crystal driving IC is mounted on a flexible printed board comprising a wiring pattern and electrode terminals to form the mounting structure which is then connected to one of the substrates of the liquid crystal device. In this case, the mounting structure can be connected to one of the substrates of the liquid crystal device by using solder.
In the above-described liquid crystal device, in some cases, a liquid crystal panel or a plastic frame functioning as a light guide for a back light is provided on the back side of the display surface of the liquid crystal substrate. In this case, the frame is possibly damaged by heating during soldering of the liquid crystal substrate and the mounting structure.
Particularly, it has recently been demanded to eliminate conventional lead-containing solder from electronic apparatuses in connection with environmental problems. In order to comply with this demand, various types of lead-free solder (binder alloys substantially not containing lead) have already been developed. However, conventional lead-containing solder has a melting point of about 183xc2x0 C., while lead-free solder has a melting point of about 210 to 230xc2x0 C. Therefore, the substitution of lead-free solder for conventional solder increases the occurrence probability of damage to the frame or deteriorates the degree of the damage to the frame because the melting point is increased. For these reasons, a conventional manufacturing process cannot be used as it is, necessitating a change of the manufacturing process in some cases.
Accordingly, the present invention has been achieved for solving the above problems, and an object of the present invention is to provide a structure and a manufacturing method capable of preventing thermal damage to a frame in an electro-optical device such as a liquid crystal device.
In order to achieve the object, in accordance with a first aspect of the present invention, an electro-optical device comprises an electro-optical panel substrate, a first wiring substrate mounted on the electro-optical panel substrate, a second wiring substrate connected to the first wiring substrate, and a frame arranged between the electro-optical panel substrate and the second wiring substrate, wherein the first wiring substrate is conductively connected to the second wiring substrate with a bonding metal, and a heat insulating layer is provided between the frame and the connection region between the first and second wiring substrates.
In the present invention, by providing the heat insulating layer between the connection region and the frame, heat transmission to the frame can be suppressed during conductive connection between the first and second wiring substrates with the bonding metal, thereby preventing damage such as thermal deformation or thermal deterioration of the frame. Also, providing the heat insulating layer prevents heat transmission from the connection region between the first and second wiring substrates to the frame to facilitate heating of the bonding metal, thereby facilitating the connecting work with the bonding metal and improving the quality of the bonded state of the connection region.
In accordance with a second aspect of the present invention, an electro-optical device comprises an electro-optical panel substrate, a plurality of first wiring substrates mounted on the electro-optical panel substrate, a second wiring substrate connected to the plurality of first wiring substrates, and a frame arranged between the electro-optical panel substrate and the second wiring substrate, wherein the plurality of first wiring substrates are conductively connected to the second wiring substrate with a bonding metal in different directions, and a heat insulating layer is provided between the frame and the connection regions between the first wiring substrates and the second wiring substrate.
In the present invention, since the plurality of first wiring substrates conductively connected to the second wiring substrate in different directions are provided, the work of conductively connecting at least one of the first wiring substrates to the second wiring substrate must be performed on the frame, and thus the heat insulating function of the heat insulating layer between the frame and the connection region becomes particularly effective.
In accordance with a third aspect of the present invention, an electro-optical device comprises an electro-optical panel substrate, a plurality of first wiring substrates mounted on the electro-optical panel substrate, a second wiring substrate connected to the plurality of first wiring substrates, and a frame arranged between the electro-optical panel substrate and the second wiring substrate, wherein the electro-optical panel substrate has a peripheral shape having a plurality of side edges, the plurality of first wiring substrates are conductively connected to the second wiring substrate with a bonding metal from the different side edges of the electro-optical panel substrate, and a heat insulating layer is provided between the frame and the connection regions between the first wiring substrates and the second wiring substrate.
In the present invention, since the plurality of first wiring substrates conductively connected to the second wiring substrate from different side edges of the electro-optical panel substrate are provided, the work of conductively connecting at least one of the first wiring substrates and the second wiring substrate must be performed on the frame, and thus the heat insulating function of the heat insulating layer between the frame and the connection region becomes particularly effective.
In accordance with a fourth aspect of the present invention, an electro-optical device comprises an electro-optical panel substrate, a plurality of first wiring substrates mounted on the electro-optical panel substrate, a second wiring substrate connected to the plurality of first wiring substrates, and a frame arranged between the electro-optical panel substrate and the second wiring substrate, wherein the first wiring substrates are conductively connected to the second wiring substrate with a bonding metal, the first wiring substrates or the second wiring substrate nearer to the frame than the connection regions between the first wiring substrates and the second wiring substrate has a thickness of about 50 xcexcm or less, and a heat insulating layer is provided between the frame and the connection regions between the first wiring substrates and the second wiring substrate.
In the present invention, the first wiring substrates or the second wiring substrate nearer to the frame than the connection regions between the first wiring substrates and the second wiring substrate has a thickness of about 50 xcexcm or less, and thus thermal deformation or thermal deterioration easily occurs in the frame due to heat of the work of conductive connection with the bonding metal. Therefore, by providing the heat insulating layer, thermal damage to the frame can be effectively decreased.
In the present invention, the bonding metal preferably comprises lead-free solder. Since the lead-free solder has a higher melting point than conventional lead-containing solder, the heat insulating layer is particularly effective.
In accordance with a fifth aspect of the present invention, an electro-optical device comprises an electro-optical panel substrate, a plurality of first wiring substrates mounted on the electro-optical panel substrate, a second wiring substrate connected to the plurality of first wiring substrates, and a frame arranged between the electro-optical panel substrate and the second wiring substrate, wherein the first wiring substrates are conductively connected to the second wiring substrate with lead-free solder, the first wiring substrates or the second wiring substrate nearer to the frame than the connection regions between the first wiring substrates and the second wiring substrate has a thickness of about 100 xcexcm or less, and a heat insulating layer is provided between the frame and the connection regions between the first wiring substrates and the second wiring substrate.
With the substrates having a thickness of about 100 xcexcm or more, damage such as thermal deformation or thermal deterioration easily occurs in the frame because the lead-free solder has a higher melting point than conventional solder. Therefore, in the present invention, the heat insulating layer is particularly effective, and with the substrates having a thickness of about 50 xcexcm or less, a significant effect is obtained.
In the present invention, the lead-free solder preferably comprises an alloy selected from the group consisting of Snxe2x80x94Agxe2x80x94Cu system, Snxe2x80x94Agxe2x80x94Bixe2x80x94Cu system, Snxe2x80x94Ag system, Snxe2x80x94Cu system, Snxe2x80x94Bi system, and Snxe2x80x94Zn system alloys.
In the present invention, the frame preferably comprises a synthetic resin material. From the viewpoint of manufacturing cost, the frame preferably comprises a synthetic resin material, for example, plastic. In this case, thermal deformation or thermal deterioration easily occurs due to heat transmitted from the connection regions, and thus the present invention particularly effective.
In the present invention, the heat insulating layer preferably has lower thermal conductivity than the material of the first or second wiring substrate arranged nearer to the frame than the connection regions. By using the heat insulating layer having lower thermal conductivity than the material of the substrates, the thickness of the heat insulating layer can be decreased to increase the degree of design freedom of a liquid crystal device and thin the entire device.
In the present invention, the heat insulating layer preferably contains a material selected from the group consisting of silicone rubber, polytetrafluoroethylene, polychlorotrifluoroethylene, and fluorocarbon rubber. All these materials have a good heat insulating property.
In the present invention, the heat insulating layer preferably has a bonding function. Since the connection portion of the first wiring substrate or the second wiring substrate is bonded to the frame with the heat insulating layer provided therebetween to eliminate the need to provide another fixing means and enable temporary fixing of the connection portion of the first wiring substrate or the second wiring substrate to the frame in the work of connecting the first wiring substrate to the second wiring substrate.
In the present invention, the heat insulating layer preferably contains a thermosetting resin. With the heat insulating layer containing the thermosetting resin, the heat insulating layer can be cured by heat receivable during the connection between the first wiring substrate and the second wiring substrate, thereby improving the connection operation and firmly fixing the connection portion of the first wiring substrate or the second wiring substrate to the frame. Furthermore, the connection portion of the first wiring substrate or the second wiring substrate can be temporary fixed to the frame by using adhesiveness before curing by heat.
In the present invention, the heat insulating layer is preferably formed to have the function to reflect light to the electro-optical panel substrate side. With the heat insulating layer having the light reflecting function, the heat insulating layer can be used as a portion of illumination means such as a back, thereby eliminating the need to provide another reflecting layer.
In the present invention, the frame has a light guide function in some cases. In the case of the frame having a light guide function, thermal deformation or thermal deterioration in the frame influences the function to illuminate a liquid crystal panel. Therefore, the present invention capable of preventing thermal damage to the frame is particularly effective.
A liquid crystal device of the present invention comprises any one of the above-described electro-optical devices of the present invention, wherein the electro-optical panel substrate serves as a liquid crystal panel substrate.
A method of manufacturing an electro-optical device comprising an electro-optical panel substrate, a first wiring substrate mounted on the electro-optical panel substrate, a second wiring substrate connected to the first wiring substrate, and a frame arranged between the electro-optical panel substrate and the second wiring substrate of the present invention comprises applying heat to the connection region between the first wiring substrate and the second wiring substrate with a heat insulating layer provided between the connection region and the frame to conductively connect the first wiring substrate to the second wiring substrate.
In the present invention, in conductively connecting the first wiring substrate to the second wiring substrate with a bonding metal, heating to a high temperature is required for melting the bonding metal, and thus the present invention is particularly effective.
The present invention is particularly effective when the first wiring substrate or the second wiring substrate provided nearer to the frame than the connection region has a thickness of about 50 xcexcm or less.
In the present invention, the use of lead-free solder as the bonding metal exhibits a significant effect because the lead-free solder has a higher melting point than conventional lead-containing solder.
In the present invention, a significant effect is obtained particularly when the first wiring substrate or the second wiring substrate provided nearer to the frame than the connection region has a thickness of about 100 xcexcm or less.
In the present invention, the lead-free solder preferably comprises an alloy selected from the group consisting of Snxe2x80x94Agxe2x80x94Cu system, Snxe2x80x94Agxe2x80x94Bixe2x80x94Cu system, Snxe2x80x94Ag system, Snxe2x80x94Cu system, Snxe2x80x94Bi system, and Snxe2x80x94Zn system alloys.
In the present invention, the frame preferably comprises a synthetic resin material.
In the present invention, the heat insulating layer preferably has lower thermal conductivity than the base material of the first or second wiring substrate arranged nearer to the frame than the connection region.
In the present invention, the heat insulating layer preferably contains a material selected from the group consisting of silicone rubber, polytetrafluoroethylene, polychlorotrifluoroethylene, and fluorocarbon rubber.
In the present invention, the second wiring substrate is preferably bonded to the frame by the heat insulating layer which receives heat during conductive connection between the first wiring substrate and the second wiring substrate. By bonding the second wiring substrate to the frame during conductive connection, another work of maintaining the second wiring substrate to the frame can be made unnecessary.
In the present invention, during conductive connection between the first wiring substrate and the second wiring substrate, the heat insulating layer is preferably thermally cured by heating to bond the second wiring substrate to the frame.
In the present invention, in some cases, a plurality of the first wiring substrates is connected to the second wiring substrate in different directions.
In the present invention, in some cases, a plurality of the first wiring substrates are connected to the second wiring substrate from different side edges of the second wiring substrate having a peripheral shape having a plurality of side edges.
In the present invention, the heat insulating layer is preferably removed after conductive connection between the first wiring substrate and the second wiring substrate. This removal of the heat insulating layer after conductive connection enables free selection of the material and thickness of the heat insulating layer of the liquid crystal device. Also, the heat insulating layer can be repeatedly used many times to decrease the manufacturing cost.
In the present invention, as the heat insulating layer, a layer having the function to reflect light to the electro-optical panel substrate side is preferably used.
As the heat insulating layer, a layer having the function to scatter light to the electro-optical panel substrate side is preferably used.
As the frame, a frame having a light guide function is preferably used.
The method of manufacturing a liquid crystal device of the present invention is the above-described method of manufacturing an electro-optical device, wherein the electro-optical panel substrate serves as a liquid crystal panel.
An electronic apparatus of the present invention comprises any one of the above-described electro-optical devices, and control means for controlling the electro-optical device.
An electronic apparatus of the present invention comprises the above-described liquid crystal device, and control means for controlling the liquid crystal device.